This invention relates to the field of radio frequency (RF) heating presses, and, more particularly to high frequency energy absorbing apparatus to be used in connection with RF heating presses.
Prior to the present invention various methods of screening and enclosing high frequency equipment that have been in use. Screened enclosures have been frequently used. Such enclosures are costly and interfere with the flow of materials used in production.
Metallic enclosures that open and close with the application of the radio frequency power and which, in the closed position, completely surround and shield the high frequency radiating components have been proposed. Such enclosures interfere with the flow of material or continuously flowing stock, add great expense and complexity to the machines and have been found not to be very effective in terms of suppressing unwanted radiation.
There are several reasons for suppressing unwanted high frequency radiation, including but not limited to: (1) the radiated diminished energy efficiency; (2) the radiated high frequency energy may interfere with radio receiving equipment located even at great distances from the heating equipment, mainly due to the content of harmonics in the radiated energy; (3) the radiated energy may represent a health hazard to personnel working at or near the machine if certain levels of radiated energy expressed in milliwatts per square centimeter exceed certain threshold levels established by the National Institute for Occupational Safety and Health Administration Notice CPL-2-2 o-Non-ionizing Radiation Citations, dated Sept. 4, 1979; (4) the wasted radiated high frequency energy may unnecessarily heat sections of the machine components which may be touched by the machine operator and cause burns or discomfort; and (5) the wasted energy may cause arcing between various machine elements and cause reduced life, e.g. piston rings may arc against cylinder walls and create burns.